UAV and LIDAR surveys were conducted of a 5-acre site to compare elevation measurements. The UAV survey had a vertical RMSE of 7 cm and captured 271 images at 60m altitude. The LIDAR data had a resolution of 1m and vertical RMSE of 8cm after correction. Comparisons showed the UAV and LIDAR elevations varied by less than 10cm at control points and had a 90% correlation at 100 verification points, demonstrating the surveys produced comparable results.

1. Terrain Model Comparison of Data
from LIDAR and UAV Imagery
One of the questions we frequently hear when talking to clients about
producing digital terrain models (DTMs) from unmanned aerial vehicle
(UAV) imagery is: “How do DTMs from drones compare with LIDAR-
derived datasets?” We wanted to be able to answer this question using
data from our own flights. Therefore, in November 2015, we flew a small
site in the city of West Linn, Oregon, with the purpose of quantifying
elevation differences between UAV and LIDAR-derived datasets.
The UAV survey was located on the western edge of a local school (Figure 1 ).
The site has a mix of flat and gently sloping terrain and is unencumbered by
vegetation. LIDAR data for the site was obtained from a 2015 flight commissioned
by the Oregon Department of Geology and Mineral Industries.
For the UAV flight, we utilized a real-time kinematic (RTK) survey to establish
20 ground control points that had an average vertical root mean square error
(RMSE) of 4 centimeters. The UAV flight captured 271 images at 60 meters above
ground level (AGL) covering 5 acres with an average side and front overlap of
80%. The resulting terrain model from the UAV imagery is depicted in Figure 2.
To account for differences in the ground sampling resolution and geoid
corrections applied to the LIDAR and UAV elevation data, the LIDAR data
was resampled and aligned with the UAV elevation model using ArcGIS
geoprocessing tools. This allowed for a common basis for comparing the
systematic deviations in the UAV elevations measurements with the systematic
deviations of the LIDAR data. Results showed that the UAV and LIDAR
surveys are producing similar results, with variations of both systems less
than 10 centimeters relative to the surveyed control points (Figure 3).
Study details:
• LIDAR resolution: 1 m
• UAV resolution: 2 cm
• UAV vertical RMSE: 7 cm
• Corrected LIDAR vertical RMSE: 8 cm
• Number of verification points: 100
• Number of ground control points: 20
• Correlation between LIDAR and UAV measured elevations at verification points: 90%
T E C H N I C A L B R I E F A S S E S S M O N I T O R
Figure One: Aerial Orthoimagery
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Figure 2: Digital Terrain Model
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T E C H N I C A L B R I E F A S S E S S M O N I T O R
In addition to comparing the results of the UAV flight
to the LIDAR data at the ground control locations,
the results were compared at 100 randomly generated
verifications points within the survey extent. This
analysis showed a 90% correlation of the relative UAV
elevations to those measured by LIDAR (Figure 4).
Locations where the two measurement approaches
differ significantly tended to be in areas with heavy
vegetative cover and near features with sharp vertical
relief, such as the backstop of the baseball field.
Our analysis shows that relative elevation measurements
obtained by the two systems for this site are comparable.
Systematic variations within the data obtained from
the two methodologies were within the documented
precision level of the LIDAR flight. Although
LIDAR-equipped fixed-wing aircraft have natural
advantages in their ability to cover large areas, for
smaller sites where high-resolution topographic
data is required, UAVs and RTK can provide a cost
effective alternative to LIDAR with similar accuracy.
About Sitka FlightPath™
To complement our systems design and data management
expertise, Sitka offers FlightPath for surveying terrestrial
and aquatic habitats using UAVs. In a single flight, Sitka
is able to collect all the data needed to provide you with
detailed, high-resolution 2D orthoimagery, topographic
datasets, metrics and more.
Figure 4: LIDAR Versus
UAV Correlation
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Figure 3: Control and
Verification Points
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